Liquid refrigerant return system



Nov. 21, v1967 M. w. GARLAND; ETL

I JQUID REFRIGERANT RETURN SYSTEM Filed April ll, 1966 D OZmJOm.

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ATTORNEY United States Patent O 3,353,367 LlQUID REFRIGERANT RETURN SYS'IIEM Milton W. Garland, Franklin County, Pa., and R 1chard A.

Peard, Spring Valley, Md., assignors to Frick Cornpany, Waynesboro, Pa., a corporation of Pennsylvania Filed Apr. 11, 1966, Ser. No. 541,826 14 Claims. (Cl. 62-115) ABSTRACT F THE DISCLOSURE A liquid refrigerant return system for returning separated liquid refrigerant into a vapor-liquid cycle refrlgeration system which comprises a reservoir means connected to receive separated liquid refrigerant from the low pressure portion of the refrigeration system and a receiver means connected to the reservoir means to receive liquid refrigerant from the latter and connected to high pressure portion of the refrigeration system to pass liquid refrigerant into the latter. Valve means is provided for isolating the receiver means from the high pressure portion of the refrigeration system when the receiver means is receiving refrigerant from the reservoirA and for communicating the receiver means with the high pressure portion when the receiver means ceases to receive refrigerant. The receiver means is maintained by a vent means at a predetermined pressure intermediate of the pressures of the high and low pressure portions of the refrigeration system upon isolation of the receiver means.

The invention relates to apparatus for and method of returning to a refrigeration system liquid refrigerant separated from gaseous refrigerant.

In compression refrigeration systems employing a volatile liquid-vapor cycle, wherein liquid refrigerant may be carried along with the vaporized or gaseous refrigerant to the compressor, it is necessary, in order to protect the compressor from damage, to separate the liquid and gaseous refrigerant, collect the separated liquid refrigerant and return the separated liquid refrigerant to the system. Many methods and means have been devised to return the liquid refrigerant to the system. Several such return systems are disclosed in the following United States patents:

The various liquid return systems heretofore devised have proven to have one 'or more of the following disadvantages; complexity, expensiveness, unreliability and imposition of unduly high thermal shocks on some of the components of the refrigerating system.

Accordingly, -it is one of the objects of the present invention to provide a liquid refrigerant return system `which is relatively simple, reliable and efficient in opera- 'tion and relatively inexpensive.

p ice Another object of this invention isto provide an improved liquid refrigerant return system which increases the operative life of the refrigerating system in that the thermal shocks imposed on the refrigerating system are substantially minimized as compared with heretofore known return systems.

A further object of the present invention is to provide a liquid refrigerant return system which automatically functions to return the liquid refrigerant under control of a single control means.

In view of the foregoing, the present invention contemplates a novel liquid refrigerant return system for a compression refrigerating system using a volatile liquidvapor cycle and having a high pressure portion for conducting high pressure liquid and vaporized refrigerant and a low pressure portion connected to receive liquid refrigerant from the high pressure portion and vaporize at least part of the liquid refrigerant. The liquid refrigerant return system comprises a separating or trap means in the loW pressure Iportion of the refrigerating system to separate the liquid and gaseous refrigerant iiuid. A reservoir means is connected to the `separating or trap means to receive the separated liquid refrigerant and to collect the liquid refrigerant. A receiver means is connected to the reservoir means to receive from the latter liquid refrigerant and to the high pressure portion of the refrigerating system to return separated liquid refrigerant to the system. Preferably the receiver means is connected into the high pressure portion of the refrigerating system at a primary receiver which forms a part of the refrigerating system. A flow control means, including level sensing members, lines and valves, are provided for causing liquid refrigerant to flow from the reservoir means into the receiver or trap means when liquid refrigerant collected in the reservoir means reaches a predetermined amount and for ceasing such flow to the receiver means when the liquid refrigerant collected falls to a predetermined amount. A valve means is provided in the connection between the receiver means and the high pressure portion of the refrigerating system for isolating the receiver means from the high pressure portion when the receiver means commences to receive refrigerant from the reservoir means and for communicating the receiver means with the high pressure portion when the receiver means ceases to receive refrigerant from the Areservoir means. To minimize the thermal shocks on the refrigerating system when the valve means communicates the receiver means with the high pressure portion of the system, a vent means is connected to the receiver means for maintaining the receiver means at a predetermined pressure .intermediate of the pressures of the high and low portions of the refrigerating system upon isolation of said receiver means from the high pressure portion of the system.

The above mentioned and other objectives and advantages of the present invention will appear more fully hereinafter from a consideration of the detailed description which follows when taken together with the accompanying drawing wherein one embodiment of the invention is illustrated.

The liquid refrigerant return system or means, in accordance with the present invention, is shown in the accompanying schematic drawing as applied to a conventional compression refrigeration system using a volatile liquid-vapor cycle. The refrigeration system comprises two portions: ia high pressure portion or side and a low pressure or suction portion or side.

As shown, the refrigeration system comprises a cornpressor which receives gaseous refrigerant from the low pressure portion of the system, compresses the gaseous refrigerant and discharges the compressed gaseous refrigerant into a discharge line 11 which forms part of the high pressure portion of the refrigeration system. From line 11, the high pressure, gaseous refrigerant is passed into a condenser 12. The condenser, which may be of the shell and tube type, is connected, through lines 13 and 14, to respectively receive cooling uid, such as Water, from a suitable source thereof, as for example a cooling tower, and pass heated cooling huid therefrom after it has passed in indirect heat exchange relationship with the gaseous refrigerant to absorb heat from the latter and thereby condense the gaseous refrigerant. From condenser 12, the condensed, liquid refrigerant is conducted to a primary or system receiver 15 via a line 16. Liquid refrigerant is conducted, as demanded by the load, from primary receiver 15, through a line 17, to an evaporator 18. To insure that only liquid refrigerant will pass into line 17, line 17 is connected to one end of a dip tube 19 which communicates at its opposite end with the interior of primary receiver 15 adjacent the bottom thereof. Flow of liquid refrigerant into evaporator 1S is controlled by a conventional expansion valve 20. Actuation of expansion valve 26 is controlled by a bulb 21 which is attached to the outlet of evaporator 13 to sense load or demand in terms of temperature. The bulb 21 is connected through line 22 with expansion valve 2) to effect actuation of the valve in response to demand or load.

The evaporator 18 forms part of the low pressure or suction portion or side of the refrigeration system and is connected to an outlet line 23. Since all of the liquid refrigerant passing through evaporator 1S may not be vaporized and the compressor 10 is not capable of accepting liquid refrigerant without risk of damage, the liquid refrigerant must be separated from the gaseous or vaporized refrigerant before the refrigerant flows to compressor 10. To achieve this separation a separator and trap 24 is provided to receive refrigerant from outlet line 23. Separator and trap 24 may be of any suitable construction which effects separation of liquid and gaseous refrigerant by centrifugal means, impact means or otherwise and collects the separated liquid refrigerant. From separator and trap 24, the gaseous refrigerant is conducted to compressor 10 by way of suction line 25 which communicates at one end with the interior of separator and trap 24 and at the opposite end with the inlet ports of compressor 10.

The improved means or system for returning the liquid refrigerant to the refrigeration system according to this invention comprises a reservoir means or collecting drum 26 and an auxiliary receiver 27 connected to each other and the high and low pressure portions of the refrigerating system in a unique manner as will be more fully explained hereinafter.

Collecting drum 26 is connected to the bottom of separator and trap 24 by `a line or conduit 2S to provide for the -gravitational flow of liquid refrigerant from the separator and trap into collecting dru-m 26.

Auxiliary receiver 27 is preferably disposed above primary receiver 15 and is connected to receive liquid refrigerant from collecting drum 26 by a line or conduit 29 which communicates at one end with the bottom of the collecting drum and at the opposite end with the top of auxiliary receiver 27. A line or conduit 30 interconnects auxiliary receiver 27 with the primary receiver 15 in the high pressure portion of the refrigeration system to provide for How of refrigerant from auxiliary receiver 27 to the primary receiver 15.

To utilize the pressure differential between the high and low pressure portions of the refrigeration system to cause flow of refrigerant from collecting drum 26 into auxiliary `receiver 27 by way of conduit 29, a line 31 is connected at one end to primary receiver 15 to receive high pressure, gaseous refrigerant and at the opposite end to collecting drum 26 to discharge the high pressure, gaseous refrigerant into the upper portion of the collecting drum. For providing control of flow through line 31 a valve 32 of any suitable auto-matic type, such as a solenoid valve, is disposed in line 31.

For control of flow through conduits 2S and 3G, pressure regulated or controlled valves 33 and 34 are disposed respectively in conduits 23 and 30. To automatically effect closing of valves 33 and 34 when valve 32 is open and allowing flow of high pressure, gaseous refrigerant, valves 33 and 34 are connected to line 31 downstream from valve 32 via lines 3S and 36, respectively.

In accordance with the present invention, auxiliary receiver 27 is maintained under a predetermined pressure intermediate of the pressure in the high and low pressure portions of the system when refrigerant is being collected in the auxiliary receiver. To impose and maintain this predetermined intermediate pressure in auxiliary receiver 27, a vent means 37 is provided. Vent means 37 comprises a line 38, an a-utomatic valve 39, such as a solenoid valve and a pressure regulated valve 40. Line 38 is connected at one end to communicate with the upper interior portion of auxiliary receiver 27 and at the opposite end with the low pressure portion of the refrigeration system. As shown in the drawing, line 38 may be connected to the separator and trap 24. The valves 39 and 40 are dis posed in line 38 with valve 39 acting as the primary control of iiuid flow through line 38 and valve 40 which is positioned between valve 3-9 Vand auxiliary receiver 27 functioning as a secondary control of fluid flow through the line. Valve `40 is of conventional back pressure valve construction and is adjusted to actuate to an open position when the pressu-re in the auxiliary receiver and line 38 exceeds a predetermined maximum value intermediate the pressures in the high and low pressure portions of the refrigeration system and to close when the pressure falls below that predetermined pressure.

After collecting drum 26 has been brought under high pressure by communication with high pressure, gaseous refrigerant to effect flow of refrigerant from the collecting drum, the collecting drum 26 is returned to the low or suction pressure of the refrigeration `system by a Vent means comprising a line 41 connected yat one end to line 31 downstream of valve 32 and at the opposite end to the low pressure portion of the refrigeration system. Control of ow of fluid, -through Vent line 41, is achieved by an automatic valve 42, such as a solenoid valve, which is disposed in the vent line. Vent line 41 also functions to relieve valves 33 and 34 of high pressure, gaseous refrigerant so that valves 33 and 34 can return to an open position. To prevent back ow of refrigerant through conduit 29 into collecting drum 26 when the latter is being vented through lines 31 and 41, a check valve 48 is disposed in conduit 29.

To provide automatic operation and control of the refrigerant return system thus far described, a single control means is provided. The control means comprises a sensing unit 43 which may be of any suitable construction capable of sensing both a predetermined maximum amount yof liquid refrigerant and predetermined minimum amount of liquid refrigerant in collecting drum 26 and to transmit an appropriate signal to effect actuation of the valves. For purposes of illustration, the sensing unit 43 is shown as having an upper liquid level, electrical switch member 44 and a lower liquid level, electrical switch member 45. Switch members 44 and 4S are connected through equalizing lines 46 and 47 to collecting drum 26 to sense liquid level in the collecting drum. Each of the switch members 44 and 45 are connected to a source of electrical current (not shown) and to automatic valves 32, 39 and -42 to effect appropriate actuation of the Valves -as hereinafter fully explained.

When switch member 44 senses that the liquid refrigerant in collecting drum 26 reaches a predetermined maximum level, and is actuated thereby, valves 32 and 39 are caused to open while valve 42 is simultaneously closed. When switch member 45 senses that the liquid refrigerant has fallen to ya predetermined minimum level, and is actuated thereby, valves 32 and 39 are caused to close while valve 42 is simultaneously opened.

To trap and remove lubricating oil from the refrigerant, which lubricant separates from the refrigerant in auxiliary receiver 27, auxiliary receiver 27 is provided with a sump 49 and a valved drain line 55 which returns the oil to the compressor oil reservoir (not shown) or other suitable place.

The liquid refrigerant return system, as herein described, functions to return liquid refrigerant to the refrigeration system with substantially minimized thermal shocks to the refrigeration system as hereinafter set forth.

With valves 33, 34 and 42 open and valves 32 and 39 closed, separated liquid refrigerant is flowing from separator and trap 24, through conduit 28 into collecting drum 26 and any liquid refrigerant in auxiliary receiver 27 is returning into the refrigeration system via conduit 30 and primary receiver 15. Liquid refrigerant continues to be accumulated in collecting drum 26 until the level of liquid refrigerant in the collecting drum reaches a predetermined maximum level as sensed by electric switch member 44. When the yswitch of switch member 44 is actuated, it causes valve 32 to be actuated to an open position and, simultaneously, valve 42 to close and valve 39 to open. At this time auxiliary receiver 27 is at the same high pressure as primary receiver so that valve 40 is actuated to an lopen position and, since valve 39 is open, the interior of auxiliary receiver 27 is bled down to the predetermined pressure value for which valve 40 is set. With valve 32 open, high pressure, gaseous refrigerant flows from primary yreceiver 15, through line 31, into vthe upper lportion of collecting drum 26. In an ammonia refrigeration system the gaseous refrigerant in primary receiver 15 may be at `approximately 197.2 p.s.i.g. (+100 F.) while the liquid in collecting drum 26 is at approximately 3.6` p.s.i.g. F.) which is the presure value of the low pressure portion of the refrigerating system. Since the gaseous refrigerant is at a substantially higher pressure than the liquid refrigerant in the collecting drum and the pressure in auxiliary receiver 27 has been reduced below the primary receiver pressure, the liquid refrigerant is forced from collecting drum 26, through conduit 29, into auxiliary receiver 27. Simultaneous with flow of high pressure, gaseous refrigerant ow into the collecting drum 26, high pressure, gaseous re frigerant flows to valves 33 and 34, through lines 35 and 36, to thereby cause valves 33 and 34 to move to a closed position. The closing of valves 33 and 34 cuts off auxiliary drum 27 from the high pressure portion or side of the refrigeration system and from the low pressure por tion of the system except through line 38. As the liquid refrigerant flows into auxiliary receiver 27, the residual vaporized or gaseous refrigerant therein will be pressurized, thereby tending to increase the pressure in the auxiliary receiver. When the pressure in the auxiliary receiver increases to a value in excess of a predetermined pressure value intermediate the pressures of the low and high portions of the refrigeration system, as for example, 58.6 p.s.i.g. (-l-40 F.), back pressure valve 49 automatically opens to pass gaseous refrigerant into separator and trap 24, through line 3S, and thereby vent auxiliary receiver 27 and relieve the pressure therein. Valve 40 by opening and closing, in response to pressure changes, maintains the pressure in auxiliary receiver 27 at the desired predetermined intermediate pressure.

When the liquid refrigerant level in collecting drum 26 reaches a predetermined minimum level as sensed by electrical switch member 45, valves 32 and 39 are caused to actuate to a closed position and valve 42 to move to an open position. With valve 32 closed to prevent flow of high pressure gaseous refrigerant and valve 42 open to vent lines 35 and 36 and collecting drum 26, valves 33 and 34 are thereby permitted to return to an open position. As previously mentioned, back ow of refrigerant through conduit 29 is prevented by check valve 48. At this stage or cycle of Voperation auxiliary receiver 27 is isolated from the low pressure portion `or side of the refrigerating system and is in communication, through line 30, with the high pressure portion at the primary receiver 15. The restoration of communication between receivers 15 and 27 by opening of valve 34, causes an increase in pressure in auxiliary receiver 27 until it reaches the system high pressure in primary receiver 15. Since the auxiliary receiver with valve 34 open forms part of the high pressure lportion of the refrigeration system, the liquid refrigerant delivered to auxiliary receiver 27 is returned to the refrigeration system. It is evident that because the pressure of the liquid refrigerant being returned in auxiliary receiver 27 is at a pressure closer to that in primary receiver 15 at the time of the opening of valve 34, the thermal shock to the refrigeration system is considerably less than in other systems. While the pressure in the auxiliary receiver 27 exceeds the predetermined intermediate pressure, when in communication with the primary receiver 15, so that valve 40 is in an open position, fluid cannot flow through line 38 because valve 39 is closed.

With valve 33 returned to its normal open position and collecting drum 26 pressure returned to low system pressure through vent line 41, collecting drum 26 is now lready to receive and accumulate additional quantities of liquid refrigerant separated and trapped in separator and trap 24. The newly `accumulated liquid refrigerant is returned to the refrigeration system in the same manner as previously described.

From the foregoing disclosure, it can be readily seen that an improved refrigerant return system has been provided which is of relatively simple construction and wherein thermal shocks to the refrigeration system are substantially minimized. In addition, it is a liquid return system which is completely automatic, the operation of which is controlled by a single control assembly.

Although -but one embodiment of the invention has been illustrated and described in detail, it is to be expressly understood that the invention is not limited thereto. Various changes can be made in the arrangement of parts without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art.

What is claimed is:

1. In a compression refrigeration system using a volatile liquid-vapor cycle and having a high pressure portion connected to conduct vaporized and liquid refrigerant and a low pressure portion constructed and arranged to receive liquid refrigerant from the high pressure portion and evaporate at least a portion of such liquid refrigerant, a liquid refrigerant return means comprising,

(a) separating means in said low pressure portion to separate liquid and gaseous refrigerant fluids,

(b) reservoir means communicating with said separating means to receive and collect liquid refrigerant,

(c) receiver means connected to said reservoir means to receive liquid refrigerant from the latter and to the high pressure portion of the refrigerating system to return separated liquid refrigerant to the system,

(d) ow control means for causing liquid refrigerant to flow from the reservoir means into the receiver means when liquid refrigerant collected in the reservoir means reaches a predetermined amount for ceasing such ow to the receiver means when the liquid refrigerant collected falls to a predetermined amount,

(e) valve means for isolating the receiver means from 7 the high pressure portion of the system when the receiver means is receiving refrigerant from the reservoir means and for communicating the receiver means with the high pressure portion when the receiver means ceases to receive refrigerant from the reservoir means, and

(f) vent means connected to said receiver means for maintaining the receiver means at a predetermined pressure intermediate of the pressures of the high and low portions of the refrigerating system upon isolation of said receiver means from the high pres sure portion of the system.

2. The apparatus of claim 1 wherein said flow control means comprises a line communicating the reservoir means with the high pressure portion of the system to receive from the latter high pressure vaporized refrigerant and valve means in said line responsive to open upon the liquid refrigerant reaching a predetermined amount and to close when the liquid refrigerant reaches a predetermined minimum amount in the reservoir means.

3. The apparatus of claim 1 wherein said vent means comprises a line communicating at one end with the receiver means and at the other end with the low pressure portion of the system and a pressure responsive valve in said line adjusted to pass refrigerant vapor from the receiver means to the low pressure portion at said predetermined intermediate pressure to thereby maintain such intermediate pressure in the receiver means.

4, The aparatus of claim 1 wherein said valve means for alternately isolating the receiver means from and communicating the receiver means with the high pressure portion of the refrigerating system is a pressure responsive valve operable to a closed position when liquid refrigerant commences to flow from the reservoir means to the receiver means and to an open position when the liquid refrigerant ceases to flow to the receiver means.

5. In a compression refrigeration system using a volar tile liquid-vapor cycle and having a high pressure portion connected to pass liquid and vaporized refrigerant and a low pressure portion constructed and arranged to receive liquid refrigerant from the high pressure portion and evaporate at least a portion of such liquid refrigerant, a liquid refrigerant return means comprising (a) separating means in said low presure portion of the system to separate liquid refrigerant from gaseous refrigerant,

(b) reservoir means communicating with said separating means to receive and hold liquid refrigerant passed from the separating means,

(c) first conduit means communicating the reservoir means with the separating means to pass liquid r-- frigerant from the latter to the reservoir means,

(d) a receiver means,

(e) a second conduit means communicating the reservoir means with the receiver means to pass liquid refrigerant from the reservoir means to the receiver means,

(f) a third conduit means in communication at one end with the high pressure portion of the refrigeration system and at the opposite end with the reservoir means to conduct high pressure vaporized refrigerant from the high pressure portion to the reservoir means,

(g) a fourth conduit means communicating the receiver means with the high pressure portion of the refrigeration system to pass liquid refrigerant in the receiver means to the high pressure portion,

(h) valve means in each of said first, second, third and fourth conduit means to control fluid flow through the respective conduit means,

(i) means connected to said receiver means for maintaining a pressure in said receiver means at a value intermediate the pressures in the low and high pressure portions of the refrigerating system, and

(j) control means responsive to a predetermined maxi mum amount of liquid refrigerant accumulated in said reservoir means for causing valve means in said first and fourth conduits to stop flow therein and the valve means in said third conduit to allow high pressure vaporized refrigerant to ow into the reservoir means to thereby force liquid refrigerant into said receiver means,

(k) said control means responsive to a predetermined minimum amount of liquid in said reservoir means for causing valve means in said first and fourth conduits to allow ow of uid therein, the valve means in said third conduit to stop flow of high pressure vaporized refrigerant into the reservoir means and the valve means in fourth conduit means to allow flow of liquid refrigerant from the receiver means into the high pressure portion of the refrigeration system to thereby return the liquid refrigerant to the refrigeration system.

6. The apparatus of claim 5 wherein said control means comprises liquid refrigerant level sensing members connected to the valve means in the third conduit means to cause such valve means to open in response to a predetermined maximum level of liquid refrigerant and to close in response to minimum liquid refrigerant level in the reservoir means.

7. The apparatus of claim 5 wherein said means for maintaining a pressure in said receiver at a value intermediate the pressures in the high and low pressure por tions of the system comprises a vent line communicating the receiver means with the low pressure portion of the system, a control valve in the vent line connected to the control means to be actuated by the latter, and a pressure responsive valve in the vent line actuable to open at a predetermined pressure intermediate of the pressure of the high and low portions of the refrigerating system to thereby prevent the pressure in the receiver from exceeding the said intermediate pressure value.

8. The apparatus of claim 5 wherein said valve means in the first and fourth conduit means are duid pressure actuated valves which are connected to the third conduit means to receive vapor-ized high pressure refrigerant and thereby be actuated to a closed position, and wherein said valve means are vented to release the high pressure vaporized refrigerant and thereby permit the valve to actuate to an open position.

9. The apparatus of claim 5 wherein a check valve is provided in the second conduit means to prevent flow of refrigerant uid in a direction from the receiver means to the reservoir means.

M). The apparatus of claim 5 wherein the valve means in the third conduit means is a solenoid actuated valve which is connected to the control means to be actuated by the latter.

11. ri`he apparatus of claim 5 wherein said receiver is an auxiliary receiverconnected by said fourth conduit means into the high pressure portion of the system at a primary receiver which is connected to receive liquid refrigerant from a condenser forming a part of the high pressure portion of the system.

l2. A method of returning liquid refrigerant separated from the low pressure side of a refrigerating system of the volatile liquid-vapor cycle type to the high pressure side of such refrigerating system comprising the steps of (a) collecting the separated liquid refrigerant,

(b) passing separated liquid refrigerant when a predetermined amount is collected into a receiver,

(c) maintaining `the receiver at a pressure value intermediate of the pressures of the low and high pressure sides of the refrigerating system, and

(d) communicating the receiver with the high pressure side of the refrigerating system, when the amount of separated liquid refrigerant collected reaches a predetermined minimum amount so that the liquid refrigerant will thereby be returned to the refrigerating system.

References Cited UNITED STATES PATENTS 2,590,741 3/1952 Watkins 62-174 2,778,195 1/ 1957 Christensen 62-174 3,212,284 10/1965 Henderson 62-174 ,3,214,932 11/1965 Grant 62-174 3,248,895 5/1966 Mauer 62-174 LLOYD L. KING, Primary Examiner. 

12. A METHOD OF RETURNING LIQUID REFRIGERNANT SEPARATED FROM THE LOW PRESSURE SIDE OF A REFRIGERATING SYSTEM OF THE VOLATILE LIQUID-VAPOR CYCLE TYPE TO THE HIGH PRESSURE SIDES OF SUCH REFRIGERATING SYSTEM COMPRISING THE STEPS OF (A) COLLECTING THE SEPARATED LIQUID REFRIGERANT, (B) PASSING SEPARATED LIQUID REFRIGERANT WHEN A PREDETERMINED AMOUNT IS COLLECTED INTO A RECEIVER, (C) MAINTAINING THE RECEIVER AT A PRESSURE VALUE INTERMEDIATE OF THE PRESSURES OF THE LOW AND HIGH PRESSURE SIDES OF THE REFRIGERATING SYSTEM, AND (D) COMMUNICATING THE RECEIVER WITH THE HIGH PRESSURE SIDE OF THE REFRIGERATING SYSTEM, WHEN THE AMOUNT OF SEPARATED LIQUID REFRIGERANT COLLECTED REACHES A PREDETERMINED MINIMUM AMOUNT SO THAT THE LIQUID REFRIGERANT WILL THEREBY BE TURNED TO THE REFRIGERATING SYSTEM. 